What We're Working On: My Bath Fan

I have a mildew problem. Whoever installed the tub and tiles in my master bath used grout rather than caulk to seal the joint where the wall meets the tub, and it collects mildew just as fast as you can clean it. My plan was to scrape out the old grout and replace it with mildew resistant silicone, and I had all my tools and materials standing by. And then I stopped myself. I stopped because I realized what I really had was an airflow problem.

Whoever installed the tub also installed a heater and fan in the ceiling, but no vent. All the moisture generated by showering just sits in the room, soaking into the walls and providing the perfect tropical environment for tiny organisms to thrive. If I replaced the grout now, I’d just have to fight the micro-fauna elsewhere. No, before attacking that problem, I had to solve the underlying cause.

Bath ceiling heater


First I had to remove the existing heater. This was fairly simple, involving only a flathead screwdriver. The thing was built in stages, so I removed the cover, then the heating element and shield and finally the base, which was attached to an electrical box in the ceiling. I capped off the wires and now I had a 4 inch by 4 inch hole in the ceiling, filled up by the electrical and giving no clues as to where the framing might be. Time to cut an exploratory hole and find out what was up in my inaccessible attic.

A couple ¼-inch holes got me started, and I put a wrecking blade on my sawzall. The house isn’t old old, but I was expecting metal lath and plaster. What I found was doubled up sheets of ½-inch drywall, so I took the blade out of the reciprocating saw and used it by hand like a keyhole saw. The only disadvantage of this is you can’t use the heel of your hand to drive it through the drywall. I made a hole big enough for my hand and found that the box was suspended between two joists by a bracket. This was kinda bad news. These brackets are sandwiched between the drywall and the joist, so they have to be cut out of the way and they can still be an obstacle. Still, I found that the box was only 4 inches away from a joist on one side, so I could hang the new vent fan on that and still have it centered in the room.

Exposed wiring


At the home center I got a new fan and a kit that includes a vent cap with a flapper to keep birds out, flexible ducting and a reducer to take a 4-inch duct to 3 inches. And here’s a tip, a wall switch with a timer isn’t shelved with the other wall switches, it’s shelved in another aisle with all the other sorts of timers. I also got a crimper for a future possible sheet metal project, and caulk for the roof. Now, a bit of a confession. As I approached this project I thought, “This is a good opportunity to record what I do and write a step-by-step how-to article.” After all, I am both a DIYer and your humble Senior Editor. But at the point where I brought the new fan home, and I realized it wasn’t going to fit as a simple retrofit, the project turned into a problem solving puzzle, rather than steps another DIYer could simply follow. Of course, this is true just about any time you open up a wall or ceiling.


Using the joist as the guide for my first edge, I traced the outline of the new fan onto the ceiling. I cut out the sheetrock with the saw blade and used the sawzall to cut the bracket holding the electrical box on the short side and bent it up out of the way. My plan was to cut the hole extra-large to admit my hand and impact driver, so I could secure the fan to the joist, and then I’d repair the extra hole. A second trip to the home center, to exchange the fan for one that would seamlessly retrofit, would solve this problem, but I was determined not to go back there today.

My Discovery

With the hole cut I could see the underside of the roof, and right there in front of me was the inside of a dormer, less than a yard away, and my new plan instantly fell into place. I was going to be on the roof anyway. I’d do the rest of the install through the dormer. I moved to the roof.

The dormer lifted off easily. I didn’t remove it all the way, but hinged it up about a foot, to do as little damage to the roofing as possible. I shimmied waist deep into the attic and, with my feet sticking out of the roof and while performing what turned out to be a heck of an abb workout, I screwed the fan to the joist, wired it up to the box and secured the duct to the dormer. Then the dormer got nailed back in place and caulked and sealed like nothing ever happened. I seriously wish I had photos of this step, but I’m forced to leave it to your imagination.

Bath vent fan, retrofit.

Retro Retrofit

Back inside, the new plastic cover for the fan was a decidedly boring louvered plastic square. So I disassembled the old heater. It took an angle grinder to cut out the rivets holding the fan assembly in place, but it left behind a perfect hole for air to channel through. (I saved the fan for another future project.) With the heater parts reassembled, minus the guts, I secured the base to the ceiling and screwed the cover back in place and the after picture looks just like the before shot.

The Finale

Bath vent fan, retro retrofit.

Adding the timer was super simple. Just remove the old wall switch and plug the wires into the timer switch and set the whole thing into the wall. I cleaned up all the dust and scraps, put away my tools and took down my ladders. Then I tested the whole system by taking a much needed shower, setting the timer to run for an extra 20 minutes, and the mirror didn’t even fog up. Now I’ve gotta tackle that grout.